Linux is known for a rapid response on fixing problems with the kernel, but the individual distros often take their time with pushing changes to users. Now, one of the researchers for Google Project Zero, Jann Horn, is warning that major distros like Debian and Ubuntu are leaving their users vulnerable.

“Linux distributions often don’t publish distribution kernel updates very frequently. For example, Debian stable ships a kernel based on 4.9, but as of 2018-09-26, this kernel was last updated 2018-08-21. Similarly, Ubuntu 16.04 ships a kernel that was last updated 2018-08-27,” he wrote in a blog post.

According to Horn, the delay means that users of these distributions remain vulnerable to known exploits. Horn describes a case in which, “a security issue was announced on the oss-security mailing list on 2018-09-18, with a CVE allocation on 2018-09-19, making the need to ship new distribution kernels to users more clear. Still: As of 2018-09-26, both Debian and Ubuntu (in releases 16.04 and 18.04) track the bug as unfixed.”

Horn is also critical of Android, which only ships security updates once a month. “...when a security-critical fix is available in an upstream stable kernel, it can still take weeks before the fix is actually available to users – especially if the security impact is not announced publicly,” he wrote.

Greg Kroah-Hartman has also been critical of distributions that don’t push these changes to users. Horn warned, “The fix timeline shows that the kernel's approach to handling severe security bugs is very efficient at quickly landing fixes in the git master tree, but leaves a window of exposure between the time an upstream fix is published and the time the fix actually becomes available to users – and this time window is sufficiently large that a kernel exploit could be written by an attacker in the meantime.”